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Hard/Emergency braking question

Discussion in 'New Riders and Riding Tips' at netrider.net.au started by Deadsy, Aug 8, 2007.

  1. I practiced braking from 80km/h to a stop a few times earlier tonight, maybe ten passes or so. I was just down the street from where I live so when I came home I checked to see how hot the disc brakes would be (curiosity) and I was surprised that the front disc wasn't hot at all. It was not cold but I did not feel any heat coming from it, now when I checked the rear brake it was basically too hot to touch.

    I know there are so many experienced riders here and I would like to know if this tells you anything? Or is it just normal, due to the size difference between the discs and how one is more exposed than the other to wind and therefore cools quicker??

    And finally does anyone have any info on decent stopping distances from 80km/h (Or any speed really, and I understand that it may differ from bike to bike, but it's still something that would be good to know).

    Thanks!


     
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  2. I was able to do the emergency stop in the learners test going 50kmh. I think that's a 7 meter distance. The guy doing my test said I passed, but there was no reason to go that fast.
     
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  3. ? Dragging too much rear?

    The front disc is in the air flow so cools faster?

    Not using enough front?

    ?different brake pad compound?

    ???

    Tells us more about the bike - twin disc gpx or single? and how the ebraking felt.
     
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  4. Rears do heat up very easily, so the light use on the way home might have kept it hot. The front would have been pretty hot as well, but they do cool down quickly once you stop abusing it, < 2mins riding around sedately.

    Having said that, 10 stops even in quick succession isn't a big deal for decent brakes.

    Maybe you just weren't braking that hard.

    All guesses.
     
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  5. Thanks for the replies.
    It's a single front disc. I did a quick measurement today and I was stopping in roughly 35-40m from 80km/h. I've found articles that list stopping distances from 80km/h anywhere from 23m to 50m so...
    This is something I plan on practicing more and more. I feel that even the short amount of time I spent last night was constructive.
    I'm just trying to understand the difference in heat with the two discs. As has been said I am leaning towards too much rear brake use and not enough front.
     
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  6. Forget the 60% 40% thing you've heard about braking. On a good piece of road, with decent brakes, decent tyres and some enthusiasm the rear brakes should be doing bugger all unless you're on a particularly heavy bike.

    There is no magical amount of rear brake. If it's not locking up then it's all good, but you can certainly be pulling up quicker than that. Just practice though, like everything. Work on the front until things start to go pear shaped then back off a bit! :shock:
     
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  7. +1 Devotard.

    The setup and squeeze front and rear technique helps squat the bike, but then almost all your braking should be being done on the front. As the weight transfers forward, the rear will unload and unless you reduce the rear brake pressure, the rear will lock - this is not good. (Unless your stunting and mean to do it...)

    As to how much braking, on a stretch of road you know well, if you haven't had any chirps or skids from the front with a progressive application of brake, then you know you still have more pressure you can apply. The onset of skidding will be your limit and is the maximum deceleration your bike/brake/trye/road combination can provide you. AND JUST BEOFRE I GET NITRIDERED, skidding is not good and NOT the maximum braking - right on the edge of skidding but still with a rotating wheel is the maximum.



    An advanced ebraking technique is to also kick the gears down back to first as you brake. Clutch in, brake F, brake R, gear down - all simultaneously. That's a lot of stuff to do, but it leaves you ready for a quick take off should you need it. For this to work though, you need to keep the rear rotating so that gear shifts will take.




    I practice ebraking at somepoint every other week. I pick a road marking near my place, ride at it, and then ebrake and see whether I can pull up the bike better than the last time. The first one after a spell is always rusty, so it pays to do them often. It also helps you get to know your bike and gets you USED to the g force's so there are NO suprises when you REALLY need it.



    Good luck with it Deadsy.
     
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  8. From my experience of riding I have been using alot more front brake than back brake. At the moment im on a light bike so I dont really need alot of back brake when I do an emergency stop. When I really need to do a emergency stop I just very lightly touch the back brake. If I put pressure on the back brake it would lock the rear. So on a light bike I would be using about 90-95% front brake and 5-10% back brake.

    I hoped I helped abit.
     
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  9. as said above, your front brake will be doing most of your braking.

    What i don't agree with is changing down gears in rapid succession while emergency braking. There have been a number of cases where i've had to brake hard and then take off without completely stopping, so my suggestion to learn to change gears down a bit more gradually, so you are in a gear you can take off in at any time.
     
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  10. Ginji, let me add one caveat.

    If you have to stop, gear down.

    If you're braking as an evasive measure with no intention of stopping, then don't gear down, or go down one/two.


    The point being, once you're used to ebraking, you then add the gearing down part into your practice, that way the reptile part of the brain learns the trick and YOU don't have to think about when you need it.

    Scenario: something suddenly happens ahead and you have to slam on the anchors... you pull up in time but are in 6th. Marge Johnson, mother of the local U9's soccer striker is behind you, with half the team in the back, distracting her, and she's bearing down on you... you spot her in the mirror, you see her eyes go wide as she slams on the brakes. Do you:
    a) Click down desperately to try and get the bike out of the way.
    b) Try to take off in 6th
    c) Jump off the bike and dive for the side of the road
    d) ... it doesn't warrant mentioning.

    :-k
     
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  11. I agree that changing gears down is and should be part of every emergency braking that anyone does, but situations change, and can do so in a blink of an eye, so I feel it's better to be in the right gear at any instant of time, rather then having to go and think about changing gears up or down in order to accelerate.

    In your scenario robslavv, I'd be in first gear and ready to move off if need be, as i have changed down as i've stopped. But i wouldn't do it rapidly like is taught in the NSW pre-learners and pre-provisional. I'd be going down gears roughly dependant on my speed, but I only can do this because I know my bike well. If I was on a unfamiliar bike, I'd be changing down in fairly rapid succession.
     
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  12. ...very noble sentiment Ginji. I'm not sure why you're fixated on the right gear though - what are you worried about? Why is it better? I'm genuinely curious.

    Ok, look, I'm honestly not trying to be argumentative, but I feel I've gotta make these next comments.

    I pull my 9R up from 80km/h odd to zero in what feels like about two - three seconds and in about <25m. That's not a lot of time to assess speed (which is rapidly decellerating) and attempt to match gears... so I'm not sure how practical that noble sentiment is, especially when the 9R (?any large bore bike?) will easily go 100km/h in first... Basically that means that I can't be in too low a gear...


    I used to ride a GPX250. IIRC it revved to around 14,000rpm and I think topped out at 50km/h in 1st. So I guess it's concievable that I could be in too low a gear for a smooth resumption - which means I could conceivably compression lock or bump against the rev limiter... BUT really, If I'm braking hard, but still moving at 50km/h when I find I can get back on the gas, I'm not likely to have had enough time for my gear lever river dance to have put me in first. Maybe 3 clicks?? If I was gearing down more slowly or not at all, I'd be in too high a gear to get back on the gas and get the hell out of there.



    In an emergency brake, you're changing gears in only one direction, DOWN. Nothing to think about.


    I applaud your noble sentiment, but just incase your post muddies the water a bit for noobs, I just want to amplify the message: If you have to ebrake to a stop, but are then in too high a gear, you are not going to be able to take off quickly if you need too.
     
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  13. I was going to say something but didnt want to be pedantic about it all seeing as though every bike is different.

    For me, where I'm doing 100 in 5th (or 6th cruising) and stopping in the same time it takes me to go down through the gears its a bit of a moot point, every bloody thing is happening rapidly. Like Rob said, a 1000 is a different story.

    While it's not exactly e-braking, a bit of track riding is a good exercise for getting used to this. Coming into a hairpin, wait until the bloke right in front of you brakes, make yourself count "one-thousand" (or until you see the baby jesus) then haaaaaard on the brakes. I only mention this because it's a situation where you do indeed have to be in the right gear, and it gives you a good feel for it with a variety of different corners, braking to and from different speeds etc.
     
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  14. EBRAKES

    THE EBRAKE THING
    I am a learner I was in latrobe uni practising the ebaking technique.
    SET UP like a cat hands up and at the ready to pull cluthch and front levers in and both feet pushing down hitting down through the gears and NOT letting the clutch out until stopped and rear braking all 4 at the same time. Thats fine in the situation where you do have to come to a complete stop, checking mirrors to enalbe a quick take off.

    BUT what happens when you are in first with the clutch in and you have to aviod rather than stop is this where you can have one of those compression lock ups?

    Why was I told to revv the engine as I gear down? Can this have a bearing on being able to not completely stop and being in the right gear at the right time?
    I'm confused? Is is just learning the sounds of the bike and knowing when to revv bewteen gearing down or do you gear down with revving at all? And if you let the clutch out when braking is this classed as emergency braking? Or a more advanced braking technique?

    I think the track days are a great idea and when I get the chance I would love to do some
    I ride a VTR250 is revving when gearing down only aplicable to a V twin type bike?
     
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  15. Catluva, with the clutch in you can do whatever you like with the gears. If you click down to a low gear and then rapidly let the clutch out while you're moving with some speed, there's a good chance you could experience compression lock up unless you blip the throttle or dial in a higher throttle setting.

    Does that help???

    You need to rev as you gear down as described to you IF you let the clutch out each gear change.

    There's no need to blip if you don't reengage the engine.

    Hope this helps.
     
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  16. they taught us that at honda handeling dynamics, in an ebrake, clutch in and just tap down like a mofo, but in practise ive found this not to always be the best solution. if you dont come to a complete stop and have to evade, anything over 20km/h (on a 250, and assuming you are in first) is going to upset the bike when you turn and release the clutch at the same time. you dont need to ride the gears down, but just make sure your gear is appropraite for your speed. easier said than done i realise, but keeping track of your gear selection and speed not only helps in braking but also cornering. hitting the brakes just before entering a corner and quickley tapping down 3 gears is much quicker than spending 5 minutes setting up corner speed with engine braking. if you are on your L's, i wouldnt be trying this straight away, but still something to think about after you get a bit more twisty time under your belt.
    but yeah keep practising, a decent sports 250 will stop on a dime. go by the feel of the weight transfere when you squeeze, not just keep on squeezing, thatll lead to locking up the front!

    cheers
    dom
     
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  17. kewl now i know what bliping is.....cheers
     
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  18. on ebrake, i distributed between front/rear wheel. after many rear sliding, i learnt to release the rear before it slide, then reapplied. sometimes rear brake is not necessary. xtra caution on wet rd
     
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  19. Here is an interesting article on an advanced braking technique called threshold braking... which is basically what ebraking aspires to achieve.

    http://www.msgroup.org/TIP230.html

     
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  20. I can get my ST1100 to do this...leave a slight mark on the road without locking the wheel.

    I think that in an emergency situation that you shoud be totally focussed on stopping and not worrying about changing gears. I leave the clutch out until the last minute or stall. I dont care as long as I stop. It is an emergency after all.
    MAny bikes will actually slow sooner if the engine braking is allowed. Especially with the big v twins.

    My emergency brake procedure is rear brake>front brake> feel for rear locking and release and reapply if it does> pull in clutch just prior to stopping.
    I can pull up from 100kph in under 19 meters. This does not allow for any reaction time as I pick the brakingpoint. Let me tell ypou that the bike feels very very floaty under such heavy braking.

    Practice practice prctice








     
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